Process of electrodepositing metals of the platinum group



Patented Oct. 28, 1930 UNITED STATES PATENT OFFICE CHRISTIAN WILLIAMKEITEL, OF PERTH AMBOY, NEW JERSEY, ASSIGNOIR TO BAKER &'COMPANY, INC..A CORPORATION OF NEW JERSEY PROCESS OF ELECTBODEPOSITING METALS OE THEIPLATINUH GBO UP Ho Drawing.

shipped as articles of merchandise; to secure such .salts from which aneflicient bath for electroplating can be readily prepared; to secure.salts none of whose ingredients will have deleterious action on thedurability of IQ the solution, and will be harmlessely and readilydecomposed even if large amounts of metal are deposited from the bath,and to obtain other advantages and results as may be brought out by thefollowing description.

According to my invention, I make use of a salt of the metal to bedeposited which when decomposed by electrolysis deposits its metalelement upon the article to be plated, while the other elements of theplating salt are eliminated as gases so that the electrolyte does notaccumulate deleterious products. I have found the ammino nitrite saltsof platinum, palladium and rhodium to fulfill these requirements, andpreferably I make use of the diammino nitrites. This salt is diiiicultlysoluble in water, but is readily soluble in hot dilute ammonia wherebyit is transformed into tetrammino nitrite which is very soluble inwater.' By introducing such ammino salts into the bath forelectrodepositing and keeping it ammoniacal, the metallic concentrationof the solution can be kept constant without deteriorating the bath.

To prepare the diammino salt, taking platinum as an example. aconcentrated solution of platinum chloride or sodium platinum chlorideis taken and a slight excess of a concentrated solution of sodiumnitrite is added. This causes a change of color from orange to lightyellow or nearly colorless, and nitrous fumes are given off as a gas.Heat is applied until no more reaction-takes place, and after cooling, aslight excess of ammonia is added. The resulting precipitate is filteredand washed alkali free, and is. the desired salt, namely platinum.diammino nitrite.

To prepare an electroplating. solutionfrom the platinum diamminonitrite, 100 grams of a suitable conducting'salt, such as ammoniumnitrate or ammonium sulphate, are

Application filed July 2, 1929. Serial No. 875,582.

dissolved in one liter of distilled water containing 5% ammonia. theplatinum diammino nitrite are added, and on heating to boiling, thelatinum diammino nitrite will go into inum tetrammino nitrite.

In the electrolysis 2.2 volts or more are used. The temperature of thebath should be 95 C. or more and the solution should be kept ammoniacal,the platinum diammino nitrite being added as needed to supply platinum.It

so ution as plat- Then 20 grams of v will be noted that the hath made asabove described will contain no chloride or other halogen compound, toaccumulate and cause the bath to deteriorate, and furthermore it will benoted that in replenishin as stated, a bath containing a chloride or oter halogen compound, the same will not be increased above the originalcontent.

Plating salts for other metals of the latinum group, such as palladiumand rho ium, can be made in a way corresponding to that which has beendescribed for platinum, using palladous chloride for palladium andrhodium trichloride for rhodium, the succeeding steps being the same asin the case of latinum, within the skill of a chemist, and t e solutionor bath prepared similarly.

Other salts than chlorides vmay be used, such as sulphates, and otherdouble salts than sodium chlorides, such as ammonium chlorides, all aswill be understood by those skilled in electro-metallurgical chemistry,and the salts expressly mentioned are to be regarded merely as typicalones.

I have found that de osits from these solutions are very dense an thatthe metals can be deposited singly or an alloy deposit secured by mixingsolutions suchas havebeen described, as for example if platinum andpalladium solutions are mixed together a deposit of an alloy of the twometals will be obtained. Platinum and rhodium solutions mixed give aplatinum-rhodium alloy deposit, palladium and rhodium solutions apalladium-rhodiumalloy, and so on.

By my invention'I obtain a salt which can be most conveniently shi pedand handled, in small bulk, as compared withthe ship in and handlingofliquid solution, and which can he simply added to theelectrodeposition bath as needed to keep it at the desired strength, andwithoutin any Way deteriorating said bath. The commercial importanceofthis process of renewing the metal being deposited from the bath isvery great and it is of great commercial value.

I have found that it is possible to plate successfully from solutionsthat contain as little as one ounce and as much as ten ounces of platingsalt per gallon.

' Various substitutions of equivalents can be made in carrying out myinvention, and proportions varied, as will be understood by thoseskilled in the art, without departing from the spirit and scope of theinvention, and therefore I do not desire to be understood as limitingmyself except as required by the following claims when construed in thelight of the prior art.

Having thus described the invention, what I claim is:

1. In the electrodeposition of metals of the group platinum, palladiumand rhodium, the process of renewing the metal deposited from thesolution by adding thereto an amino nitrite of the metal being depositedand keep ing the solution ammoniacal.

2. In th electrodeposition of metals of the group platinum, palladiumand rhodium, the rocess of renewin the metal de osited from the solutionby adding thereto a iammino n trite of the metal being deposited andkeeping the solution ammoniacal. a5 3. In the electrodeposition ofplatinum, the process of renewing platinum in the solutiop y addingthereto an ammino nitrite of plannum and keeping said solutionammonlacal. 4. In the electrodeposition of platinum, the 40 process ofrenewing platinum in the solution by adding thereto a diammino nitriteof platinuzn and keeping said solution ammomacal.

5. Method for the preparation of an electrolyte for theelectrodeposition of a metal is or alloy of the group comprisingplatinum, palladium and rhodium which comprises dissolving an amminonitrite of the metal to be deposited in Water containing ammoniaand asuitable conducting salt. no CHRISTIAN WILLIAM KEITEL.

